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Q.What’s the most cost-effective way to thaw a site for excavation? We are building a 16x24-foot addition with a crawlspace underneath, and the frost is already 12 inches deep.

A.Jay Meunier, a contracting specialist at S.T. Griswold and Co., a ready-mix supplier in Williston, Vt., responds: If your excavation contractor is not equipped to tackle 12 inches of frost, the next best alternative, other than waiting until spring, is to use a ground heater. The rental fee can be somewhat expensive — about $900 per day in our area — but ground heaters can remove a lot of frost in 24 hours over a 1,500-square-foot area. These units come with a glycol tank and tubing that is laid on the frozen ground with 12 to 24 inches between tubing runs. The area is then covered with poly and insulating blankets that force the heat from the warm glycol and ground moisture downward, thus thawing the area.

In loamy and sandy soils, it’s common to thaw 12 inches of frozen ground within 24 hours. Clay and gravel tend to take longer, but I’ve been told that you can speed the process by spraying water on the area before spreading the poly and blankets.